At least seven people, including three children, have been killed by a roadside bomb near a Shia Muslim procession in north-western Pakistan.

The blast, which also wounded 30 people, happened in the city of Dera Ismail Khan, a stronghold of Sunni Muslim militant groups, according to local police.

More attacks are feared in the coming days as the minority Shia Muslims prepare to observe the holy day of Ashura on Sunday, the climax of the holy month of Muharram.

No one claimed responsibility, but the suspicion fell on Pakistani Taliban, who have carried out such attacks previously.

Ashura commemorates the death of Imam Hussein, the Prophet Muhammad's grandson, in the 7th century. The Sunni-Shia schism over Muhammad's rightful heir dates back to that time.

President Asif Ali Zardari condemned the bombing, which took place near the South Waziristan tribal region.

"Such nefarious acts cannot deter the people and the government in their fight against the scourge of militancy," he said in a statement.

Sunni extremists frequently attack Shia Muslims, who they consider heretics, and the Ashura ceremonies are a prime target.

On Wednesday night, a Taliban suicide bomber struck a Shia Muslim procession in Rawalpindi, a garrison city near Islamabad, killing 17 people. The same day, the Taliban set off two bombs outside a Shia mosque in the southern city of Karachi, killing one person and wounding 15 others.

Qamar Abbas Zaidi, the spokesman for main Shia political party, Tehrik-e-Jafariya, vowed this week to go ahead with Ashura processions across the country despite threats of attacks.

Pakistani authorities have deployed thousands of additional police across the country to heighten security for such processions.

Authorities have also suspended mobile phone service in all the major cities for two days to prevent such bombings, which officials say are often remotely detonated by mobile phones.